The disclosure of Japanese Patent Application No. 2000-280516 filed on Sep. 14, 2000 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of Invention
The invention relates generally to a braking force control apparatus and method of a motor vehicle, and more particularly to a braking force control apparatus and method of a motor vehicle including regenerative braking devices and a friction braking device for front wheels and rear wheels of the vehicle.
2. Description of Related Art
A known type of a braking force control apparatus of a motor vehicle, such as an automobile, is disclosed in, for example, Japanese Laid-open Patent Publication No. 9-93711. In the known braking force control apparatus, driven wheels are provided with a hydraulic braking device (i.e., a friction braking device), and drive wheels are provided with a regenerative braking device and a hydraulic braking device. In operation, when the regenerative braking force of the drive wheels reaches a predetermined value that is equal to or smaller than a maximum value, the regenerative braking force is kept at the predetermined value, and hydraulic braking of the driven wheels is started. With the driven wheels being hydraulically braked, the regenerative braking force applied to the drive wheels is kept at the predetermined value, until the ratio of the braking forces of the driven wheels and drive wheels becomes equal to a predetermined ratio.
The braking force control apparatus as described above makes it possible to suitably control the ratio of the braking forces of the driven wheels and drive wheels to the predetermined ratio, while performing regenerative braking of the drive wheels so that the regenerative braking force applied to the drive wheels becomes equal to the predetermined value, which in turn is equal to or smaller than the maximum value.
In the known braking force control apparatus as described above, hydraulic braking of the driven wheels is started when the regenerative braking force of the drive wheels reaches the predetermined value, and the regenerative braking force is kept at the predetermined value until the ratio of the braking forces of the driven wheels and drive wheels becomes equal to the predetermined ratio. With this type of the braking force control apparatus, however, the regeneration efficiency of the regenerative braking device cannot be maximized. To the contrary, if an attempt is made to maximize the regeneration efficiency of the regenerative braking device, the ratio of the braking forces of the driven wheels and the drive wheels cannot be controlled to the predetermined ratio.
In addition, the driven wheels of the vehicle that employs the braking force control apparatus disclosed in the above-mentioned publication are not provided with a regenerative braking device, and therefore regenerative braking is not effected, namely, electric energy is not recovered during braking of the driven wheels. Thus, the known braking force control apparatus cannot increase the regeneration efficiency of the vehicle as a whole by utilizing regenerative braking of the driven wheels, thus leaving a room for improvement in this respect.
It is therefore one object of the invention to provide a braking force control apparatus and method of a motor vehicle having regenerative braking devices and a friction braking device for front wheels and rear wheels, wherein the regenerative braking devices and the friction braking device for the front and rear wheels are optimally operated under suitable control, thus assuring an improved regeneration efficiency of the vehicle as a whole, while achieving a predetermined ratio of the braking forces of the front and rear wheels.
To accomplish the above and/or other objects, there is provided a braking force control apparatus and method of a motor vehicle including (a) first and second regenerative braking devices that are operable to effect regenerative braking with respect to front wheels and rear wheels, respectively, and (b) a friction braking device that is operable to effect friction braking with respect to each of the front wheels and the rear wheels. A controller of the braking force control apparatus calculates a first target braking force of the front wheels and a second target braking force of the rear wheels, based on a braking requirement made by a driver of the vehicle and a ratio of braking forces of the front wheels and the rear wheels. The controller initially causes the first and second regenerative braking devices to generate regenerative braking forces at the front wheels and the rear wheels, and then, if necessary, causes the friction braking device to generate a friction braking force at each of the front wheels and rear wheels, so that a total braking force applied to the front wheels and a total braking force applied to the rear wheels are controlled to the first target braking force and the second target braking force, respectively.
With the braking force control apparatus and method as described above, the overall braking force of the motor vehicle is suitably controlled in accordance with the braking requirement made by the driver or vehicle operator, and the ratio of the braking forces of the front and rear wheels is also suitably controlled to a predetermined braking-force ratio. Furthermore, the regenerative braking devices and friction control device for the front wheels and the rear wheels can be optimally operated, thus assuring an improved regeneration efficiency of the vehicle as a whole and significantly improved fuel economy, as compared with conventional braking devices controlled by a conventional braking force control apparatus.